SANTO DOMINGO -- Prominent Dominican lawyer Vinicio Castillo on Monday said allegations that linked U.S. Sen. Robert Menendez to sex parties with prostitutes in the Dominican Republic were part of a “dirty campaign” aimed at discrediting his cousin, a Florida eye doctor who has a stalled multimillion-dollar contract for security at Dominican ports.

Castillo said Monday he will formally request Dominican authorities open an investigation into the source of allegations that claimed Menendez, a New Jersey Democrat, and Florida ophthalmologist Salomon Melgen had sex parties with prostitutes, including some that were underage.

Those allegations first surfaced last year on a conservative U.S. website. The scandal gained prominence last month when the FBI raided Melgen’s South Florida offices, and Menendez’s office said he had repaid the doctor $58,000 for trips to the Dominican Republic on his private jet. The FBI is investigating the doctor and his relationship with Menendez, including their trips together.

The source of the allegations, who used the e-mail handle Peter Williams, has not come forward; neither have the prostitutes who provided videotaped interviews for the website.

Castillo, who was also named by the tipster, said his reputation has been damaged.

The Dominican National Police’s High-Tech Crimes Division “should ask for and receive help from the FBI and DEA, to establish who … put together false testimonies and documents fabricated to morally assassinate Senator Menendez” and Melgen, Castillo said, reading from a prepared statement at a press conference in his family’s Santo Domingo law offices.

Castillo called the allegations part of a “diabolical plot” orchestrated to discredit Melgen, who owns a company with a lucrative contract with the Dominican government to provide X-ray machines at ports. The machines would be used to scan shipping containers to look for contraband and illegal drugs.